This research project is involved with the following areas of investigation: The translational control of gene expression and protein synthesis, particularly as it relates to placental development and function: A. Changes in transfer RNA and aminoacyl-tRNA synthetase complements during placental development. b. Comparison of placental tRNA's and tRNA aminoacylases with those of other differentiated tissues. c. Studies on two leucyl-tRNA synthetases that exist in the placenta. d. Analysis of non-standard tRNA aminoacylation kinetics. E. Reverse phase chromatographic elution profile analysis of placental tRNA isoaccepting species. Hormonal Responsiveness of the Placenta, and the Effects and Significance of Hormones on Placental Function: A. Effect of growth hormone, insulin and chorionic somatomammotropin on amino acid transport in placental tissue slices. B. The effect of non-steroid hormones on placental cyclic AMP levels. C. Studies on hormonally inducible enzymes in the placenta with emphasis on tyrosine aminotransferase.